Field of the Disclosure
The present disclosure relates to ballast compatibility of LED lamps; more specifically, it relates to a buffer circuit for safe replacement of LED tubes with drivers in the existing ballast fixtures.
Background
LED lighting has become popular in the industry due to the many advantages this technology provides. For example, LEDs typically have a longer lifespan, pose fewer hazards, and provide increased visual appeal when compared to other lighting technologies, such as compact fluorescent lamp (CFL) or incandescent lighting technologies.
A recent generation of efficient lighting fixtures was designed for discharge lamps, such as fluorescent lamps operating with either electronic or magnetic ballasts to stabilize their operating characteristic. An electrical ballast is a device intended to limit the amount of current in an electric circuit. Many existing industrial and residential lighting systems use ballast operating lighting fixtures which, compared to the new improved technology of LED lamps, offer lower light efficiency and shorter life span. LED lamps typically include their specific driver in their tube/bulb for safe functioning with regulated current, and to maximize their lighting efficiency, with or without light dimming characteristics.
On the other hand, electronic ballasts are commonly required to stabilize operation of fluorescent lamps that are designed to operate with a specific start-up sequence. Oftentimes, they operate at high-voltage and high frequency during ignition phase before settling to low-voltage, high-frequency operation when the lamp is emitting light. If the ballast does not detect the lamp ignition, the start-up sequence will repeat.
Many end users of LED lamps want to replace their old less efficient lighting system of discharge lamps (most often fluorescent lamps) with more efficient, long lasting LED lamps. LED lamps advantageously improve lighting characteristics and reduce user's electric utility consumption and maintenance expenses. However, the barrier they face is the rewiring of the entire existing lighting fixture to remove existing ballast. In other words, switching to LED lamps is costly and necessarily involves time delay in their operation. Presently, existing plug-and-play products in the LED tube market are limited to specific applications which generally are not compatible with various ballast configurations. LED drivers are incompatible with electronic ballast because it does not present fixed impedance as seen by the ballast. Moreover, the LED driver will be subjected to continuous high-voltage input which could exceed the ratings of the circuit components, such as metal oxide varistors (MOVs), and semiconductor switching devices, such as metal-oxide field-effect transistors (MOSFETs), which may result in safety failure.
The output of an electronic ballast also has a much higher frequency (+20 kHz or higher) than ordinary AC line which, even with electromagnetic (EM) ballast, is 50 Hz or 60 Hz. Therefore, direct replacement of an LED tube in an existing lighting fixture with electronic ballast can result in fatal failure/damage of the circuit components.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.